9 02/18 NOTE: In all cases be sure that the steel end is beveled, smooth, and free of burrs. To insure proper assembly of the double bell coupling with beveled ends of pipe, follow the instructions for rubber ring joint assembly steps as given above. Then, if one beveled end is in a fixed position, such as the end length of a pipeline, mount the coupling on the fixed length first. Then, while holding the coupling firmly in this position, insert the beveled end of the free length into the coupling. TESTING: After all concrete thrust blocks have adequately cured, a hydrostatic test is applied to determine the soundness of the line. A test pressure of 50 psi over working pressure for one hour is general- ly used unless other requirements are specified. Joints should be visually inspected and proved tight. It should be noted that, entrapped air, temperature changes and slight movement of the pipe can cause variations in test pressures. These factors should be taken into consideration when testing and care taken to minimize their influence on the test results. BACKFILLING: Backfilling of trenches shall progress as rapidly as construction, testing, and acceptance of work permits. Uniformly compact and grade bottom of trenches. After installation of pipe and bedding material, backfill as follows: Place initial backfill in layers to a depth of 12 inches of the initial bedding. Compact the material to a density equivalent to the surrounding undisturbed soil or to 90 percent of maximum density (ASTM D1557, Method D), whichever is greater. Backfill remainder of trench in one-foot lifts and compact to 90 percent maximum density (ASTM D1557, Method D). For trenches excavated in roads, streets, or located under structures, place backfill in 6-inch layers to top of trench and compact each layer to at least 95 percent maximum density (ASTM D1557, Method D). FLANGED JOINTS: Flanged joints shall be faced true, provided with gaskets, and made perfectly square and tight. It should be noted that flanged joints are not recommended underground.